1. Field of the Invention
The present invention relates to a stereoscopic image display device and, more specifically, to a stereoscopic image display device which is capable of providing bidirectional stereoscopic image display that provides parallax images for at least two viewpoints each for a first direction and a second direction simultaneously and unidirectional stereoscopic image display that provides parallax images for at least two viewpoints each for either the first direction or the second direction.
2. Description of the Related Art
For example, stereoscopic image display devices for displaying images capable of providing stereopsis in apparatuses such as television sets, personal computers, smart phones, tablets, game machines, and the like have already been spread into consumer appliances.
In general, a stereoscopic image display device is constituted with a display panel in which a plurality of pixels are provided and optical modules provided by corresponding to the pixels. In a twin-lens stereoscopic image display device, light rays from the sub-pixels corresponding to each viewpoint image are inputted as different images to each of the right eye and the left eye of an observer. This provides the observer with stereopsis.
The structure of a multi-lens stereoscopic image display device is similar to that structure. However, the design of the pixels or the optical modules and output image processing are changed to increase the number of viewpoints. This makes it possible to achieve stereopsis at a plurality of viewpoints from a greater number of observers or directions. Further, an integral photography (IP) type is a device with which a space image is displayed with element images corresponding to the position of the image and a directive lens. Thus, the structure thereof is the same as that of the structure described for the two-lens and multi-lens stereoscopic image display device.
Depicted in Japanese Patent No. 4968655 (Patent Document 1) is an existing stereoscopic image display device (referred to as a bidirectional stereoscopic image display device hereinafter) which is capable of displaying parallax images in both the horizontal direction and the vertical direction of the display device. The technique depicted therein can also be applied to various types such as the two-lens type, multi-lens type, and IP type.
There are inherent issues existing with such stereoscopic image display devices. With a general display panel, there is a region (referred to as a non-control region hereinafter) existing between boundaries of sub-pixel apertures where various kinds of signal lines shield the light or control of electro-optic conversion for applied signals cannot be done. The non-control region is expanded and projected by combining the display panel and the optical module, so that the so-called 3D moiré is observed by the observer.
The “3D moiré” is periodic luminance (or color) unevenness generated when different images are projected to different angle directions, which is fluctuation of the luminance for the viewing angle directions. There are cases where it is not an issue depending on the observing position. However, when the luminance fluctuation for the viewing angle directions is large, it is considered to impose an influence that is not preferable for stereoscopic image display. Therefore, it is desirable to make the luminance fluctuation equal to or less than a prescribed value.
The “3D moiré” is notably generated particularly when the observing position is shifted. Specifically, it is notably generated when the observing position is shifted from a stereopsis region to another stereopsis region in cases of the two-lens type or the multi-lens type stereoscopic image display device. In a case of the IP type, it is notably generated when there is a change in the space image.
For lightening the “3D moiré”, there are following technical documents. Japanese Patent No. 3525995 (Patent document 2), Japanese Patent No. 4197716 (Patent document 3), and Japanese Unexamined Patent Publication 2011-164148 (Patent document 8) disclose techniques with which the aperture areas in the space separating directions within a pixel are made constant through tilting one side of the pixel obliquely, for example, and an overlapping area with neighboring sub-pixels is used in the boundary region to make the aperture areas of the pixel constant. Japanese Patent No. 3027506 (Patent Document 4) discloses a technique which suppresses the 3D moiré by designing the sub-pixels to be in a delta form.
Japanese Unexamined Patent Publication Hei 08-149520 (Patent Document 5) discloses a technique which suppresses the 3D moiré through dispersing light rays by using a diffusion sheet. Japanese Patent No. 4010564 (Patent Document 6) and Japanese Unexamined Patent Publication 2010-026499 (Patent Document 7) disclose techniques which suppress the 3D moiré by using overlapping areas of neighboring pixels by devising the shape of the sub-pixels. All of the methods depicted in Patent Documents 2 to 8 are designed to lighten the 3D moiré of stereoscopic display by mixing the image of a single viewpoint pixel with the image from other pixels.
However, it is impossible to apply the methods for lightening the 3D moiré depicted in Patent Documents 2 to 8 for the existing bidirectional stereoscopic image display device depicted in Patent Document 1. The reason is that parallax images are displayed in both the horizontal direction and the vertical direction with the bidirectional stereoscopic image display device, so that the 3D moiré is generated in four sides of a non-control region surrounding the sub-pixels. The methods depicted in Patent Documents 2 to 8 can be applied for lightening the 3D moiré in one direction. However, it is not possible with those methods to secure the luminance smoothness in the other directions. Therefore, the 3D moiré cannot be lightened.
Further, as described above, all of the methods depicted in Patent Documents 2 to 8 are designed to lighten the 3D moiré of stereoscopic display by mixing the image of a single viewpoint pixel with the image from other pixels. However, at the same time, this causes the so-called 3D crosstalk in which a display content of an image enters into another single image. In particular, the influence of the crosstalk described above becomes prominent with the bidirectional stereoscopic image display device.
This is because the boundaries between the pixels exist not only in the horizontal direction but also in the vertical direction in the bidirectional stereoscopic image display device, so that it is necessary to mix the images from the neighboring sub-pixels in both of the directions in order to overcome the 3D moiré of stereoscopic display. At this time, the stereoscopic display property is deteriorated unless mixture of the images from the sub-pixels neighboring to each other in the horizontal direction is used for the 3D moiré in the horizontal direction and mixture of the images from the sub-pixels neighboring to each other in the vertical direction is used for the 3D moiré in the vertical direction.
At the same time, with the bidirectional stereoscopic image display device, it is necessary to make the stereoscopic display image quality equivalent in any of a plurality of directions for reducing the uncomfortable feeling sensed by the observer. That is, it is necessary that the 3D moiré improved effect in the horizontal direction and the 3D moiré improved effect in the vertical direction are equivalent, and the levels of the 3D crosstalk in both directions are equivalent as well.
Patent Document 1 discloses the invention regarding the element layout in a stereoscopic image display device which displays parallax images in the horizontal and vertical directions. However, there is no statement or suggestion mentioned therein regarding the means for overcoming the 3D moiré.
As described above, the methods depicted in Patent Documents 2 to 8 can only lighten the 3D moiré in one direction, so that those methods cannot be applied to the stereoscopic image display device. For example, Patent Document 4 is designed to lighten the 3D moiré by arranging the sub-pixels in a delta layout. However, the pixels cannot be disposed in a highly dense manner with that layout. Thus, the non-control regions are increased, so that the numerical aperture cannot be improved. This is an adverse effect for achieving high luminance.
Further, with the delta layout, the closest sub-pixels are not necessarily placed by neighboring to each other along the parallax directions. Thus, the 3D moiré generated in the horizontal direction, for example, is suppressed by using the luminance compensation of the sub-pixels corresponding to the vertical parallax. Thus, with this technique, the 3D crosstalk generated in accordance with suppression of the 3D moiré is generated because of the vertical parallax images even in the horizontal direction. Therefore, fine stereopsis cannot be acquired.
It is therefore an exemplary object of the present invention to provide a stereoscopic image display device capable providing fine stereopsis by suppressing generation of the 3D moiré and influence of the 3D crosstalk even when observed from any of a plurality of directions.